From: Alvaro Herrera <alvherre@kurilemu.de>
To: Michael Paquier <michael@paquier.xyz>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: euler@eulerto.com
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: NULL pointer dereference in syslogger with load_libraries() and -DEXEC_BACKEND at startup
Date: Tue, 26 May 2026 13:09:13 +0200
Message-ID: <ahV9KzLOqvOw78C3@alvherre.pgsql> (raw)
In-Reply-To: <ahU1AIsL3QJOONRG@paquier.xyz>
On 2026-May-26, Michael Paquier wrote:
> This issue is different, it is a Postgres logic bug, so adding an
> exception like the one you are suggesting is just a shortcut hiding
> the real issue: the log file is not ready yet, but the syslogger is
> invoked at a point when it thinks the log file exists.
I think we can solve this easily by flipping a new Boolean value at the
same point were MyBackendType was previously set. The attached POC
fixes the scenario you described; can you confirm? It needs some
additional comments, of course.
(There is one more place in elog.c where we check that MyBackendType is
_not_ B_LOGGER, but I think that one is correct as-is; and I'm wondering
if that would behave correctly before 0c8e082fba8d.)
--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
“Cuando no hay humildad las personas se degradan” (A. Christie)
Attachments:0001-POC-syslogger-add-Boolean-state-indicating-readiness.patch (text/x-diff, 2.7K) download
From 3fee63b168279acb6556525b879559c03427ac14 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Herrera?= <alvherre@kurilemu.de>
Date: Tue, 26 May 2026 12:45:01 +0200
Subject: [PATCH] POC: syslogger: add Boolean state indicating readiness
This replaces a comparison of MyBackendType, which was made obsolete by
commit 0c8e082fba8d.
---
src/backend/postmaster/syslogger.c | 5 +++++
src/backend/utils/error/elog.c | 6 +++---
src/include/postmaster/syslogger.h | 1 +
3 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/src/backend/postmaster/syslogger.c b/src/backend/postmaster/syslogger.cindex acfe0a01715..d736f6a4fab 100644--- a/src/backend/postmaster/syslogger.c+++ b/src/backend/postmaster/syslogger.c@@ -76,6 +76,9 @@ char *Log_filename = NULL;
bool Log_truncate_on_rotation = false;
int Log_file_mode = S_IRUSR | S_IWUSR;
+/* for elog.c */+bool syslogger_setup_done = false;+
/*
* Private state
*/
@@ -195,6 +198,8 @@ SysLoggerMain(const void *startup_data, size_t startup_data_len)
Assert(startup_data_len == 0);
#endif
+ syslogger_setup_done = true;+
/*
* Now that we're done reading the startup data, release postmaster's
* working memory context.
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.cindex 50c53b571a0..a6936a0c664 100644--- a/src/backend/utils/error/elog.c+++ b/src/backend/utils/error/elog.c@@ -3831,7 +3831,7 @@ send_message_to_server_log(ErrorData *edata)
* pipe). If this is not possible, fallback to an entry written to
* stderr.
*/
- if (redirection_done || MyBackendType == B_LOGGER)+ if (redirection_done || syslogger_setup_done)
write_csvlog(edata);
else
fallback_to_stderr = true;
@@ -3845,7 +3845,7 @@ send_message_to_server_log(ErrorData *edata)
* pipe). If this is not possible, fallback to an entry written to
* stderr.
*/
- if (redirection_done || MyBackendType == B_LOGGER)+ if (redirection_done || syslogger_setup_done)
{
write_jsonlog(edata);
}
@@ -3885,7 +3885,7 @@ send_message_to_server_log(ErrorData *edata)
}
/* If in the syslogger process, try to write messages direct to file */
- if (MyBackendType == B_LOGGER)+ if (syslogger_setup_done)
write_syslogger_file(buf.data, buf.len, LOG_DESTINATION_STDERR);
/* No more need of the message formatted for stderr */
diff --git a/src/include/postmaster/syslogger.h b/src/include/postmaster/syslogger.hindex 30c4b2daf3f..44409fc2542 100644--- a/src/include/postmaster/syslogger.h+++ b/src/include/postmaster/syslogger.h@@ -85,6 +85,7 @@ extern PGDLLIMPORT int syslogPipe[2];
extern PGDLLIMPORT HANDLE syslogPipe[2];
#endif
+extern bool syslogger_setup_done;
extern int SysLogger_Start(int child_slot);
--
2.47.3
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To: pgsql-hackers@postgresql.org
Cc: alvherre@kurilemu.de, michael@paquier.xyz, horikyota.ntt@gmail.com, euler@eulerto.com, pgsql-hackers@lists.postgresql.org
Subject: Re: NULL pointer dereference in syslogger with load_libraries() and -DEXEC_BACKEND at startup
In-Reply-To: <ahV9KzLOqvOw78C3@alvherre.pgsql>
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